You're pretty close, although you've left out and modified a couple of crucial bits:1. Form submissions submit the *name* of the element, not the id, and that's what the endpoint is looking for. So the json object you submit needs to be:

{
"cm-fjidy-fjidy": $('#fjidy-fjidy').val()
}

2. To avoid the cross-site scripting problem, this needs to be a jsonp request (otherwise the browser won't submit anything - which is what you've found). The way to make getJSON do that is to include "callback=?" in the query string of the url, ie: